1. Field of the Invention
This invention relates generally to systems and methods for communicating via an infrared signal, and more particularly to a communication system and method utilizing an infrared signal emitter communicating a predefined signal, and an infrared signal receiver capable of receiving such predefined signal, distinguishing such predefined signal within a field of view of the infrared signal receiver, and providing output indicating the location of the infrared signal emitter within the field of view of the infrared signal receiver.
2. Background of the Prior Art
Night vision devices exist that aid a user in viewing scenery and objects that they would otherwise have difficulty viewing in darkness. Such devices function by intensifying available light. Even a small LED appears as a large, bright headlight when viewed through night vision devices, even from great distances. This effect is referred to as blooming and allows very small near infrared signaling devices, such as a Budd Light, Phoenix Light, or VIP Light, to be used as a marker or beacon for a person or object carrying such device, which marker or beacon may be readily viewed through night vision devices even from great distances. Unfortunately, however, such near infrared signaling device becomes simultaneously visible to anyone else equipped with night vision devices. If the purpose is identification of friendly forces in a combat environment, for example, it will serve little usefulness if the enemy is likewise equipped with night vision devices.
Infrared cameras, on the other hand, function by detecting differences in the amount of electromagnetic energy emitted by different objects in the field of view of the camera, in either the mid infrared or far infrared wavelengths (collectively thermal infrared), and presenting a representation of the field of view of the infrared camera on a display. There is no blooming effect with infrared cameras. Rather, the relative size of an object displayed is accurate and does not increase based on the amount of electromagnetic energy the object is emitting. This characteristic of infrared cameras has necessitated that thermal infrared marking or signaling devices be of sufficient size that they can be distinguished from all other thermal infrared sources in the field of view of the infrared camera by a person looking at the display. Particular environmental conditions and the magnification and optical quality of the infrared camera being used typically dictate the distance from which a marker or signaling device of a given size can be adequately detected by a person viewing the display. By way of example, in order to readily view a thermal infrared marking device at a distance of 4 to 5 kilometers by a currently available military infrared camera with 10-power magnification, the marking device would typically need to be in excess of 200 square inches in size. Such size requirements for distant surveillance limit the usefulness of static infrared markers.
Compounding this problem is the number of objects in the field of view of the infrared camera emitting infrared energy, including buildings, vehicles, concrete or other pavement, electrical devices, power lines, vegetation, and a long list of other items that can create hot spots in the camera's field of view. Distinguishing a thermal infrared marking or signaling device from all of the infrared sources in the filed of view can be a significant challenge. Solutions include making the thermal infrared marking device significantly large and/or arranging a number of devices in an unnatural pattern, such as the “Inverted Y” pattern used by the military for marking helicopter landing zones.
Flashing infrared emitters have also been provided for use as marking and signaling devices to allow such marking and signaling devices to be more easily distinguished from other objects in the field of view, as the flashing signal draws the attention of the person viewing the display. However, there are high costs associated with the manufacture of flashing thermal infrared emitters of sufficient size so as to enable them to be viewed from distances that would render them useful as markers and signaling devices. Moreover, even if cost were not an issue, such flashing emitters would have to be provided in such size that would render them unsuitable for use where compact size and portability are required features, such as where the device is intended for use as a portable marker or signaling device for military or law enforcement personnel.
Given these difficulties, there remains a need for a system and method enabling the observation and detection of an infrared marker and/or signaling device from a distance that maintains the usefulness of such device for its intended function, while keeping the device small enough to be portable, such as when used as a personnel marker or signaling device.